Asymmetric synthesis of quaternary α-fluoro-β-keto-amines via detrifluoroacetylative Mannich reactions

Catalytic Asymmetric Allylic Alkylation with Arylfluoroacetonitriles

A palladium(phosphinoxazoline) catalyzed method for asymmetric allylic alkylation of α-aryl-α-fluoroacetonitriles is introduced. This reaction achieves C-C bond formation and incorporation of two adjacent chirality centers with moderate to good yields, high enantioselectivities, and up to 15:1 dr.

Chiral FLP-catalyzed asymmetric hydrogenation of 3-fluorinated chromones

The asymmetric hydrogenation of fluorinated olefins is an efficient pathway towards the synthesis of chiral fluorine-containing compounds. This paper described metal-free asymmetric hydrogenation of 3-fluorinated chromones with the use of readily available achiral borane and chiral oxazoline as an FLP catalyst for the first time. A variety of optically active 3-fluorochroman-4-ones were obtained in high yields with up to 88% ee.

Catalytic stereoselective Mannich-type reactions for construction of fluorinated compounds

For its unique role in developing and designing new bioactive materials and healthcare products, fluoro-organic compounds have attracted remarkable interest. Along with ever-increasing demand for a wider availability of fluorine-containing structural units, a large diversity of methods has been introduced to incorporate fluorine atoms specially in a stereoselective fashion. Among them, catalytic Mannich reaction can proceed with a broad variety of reactants and open clear paths for the synthesis of versatile amine synthons in the synthesis of natural product and pharmaceutical molecules. This review provides an overview of the employment of catalytic asymmetric Mannich reactions in the synthesis of fluorine-containing amine compounds and highlights the conceivable distinct mechanisms.

Asymmetric Mannich reactions of (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimines with yne nucleophiles

In the present work, arylethynes were studied as new C-nucleophiles in the asymmetric Mannich addition reactions with (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimine. The reactions were conducted under operationally convenient conditions affording the corresponding Mannich adducts with up to 87% yield and 70:30 diastereoselectivity. The isomeric products can be separated using regular column chromatography to afford diastereomerically pure compounds. The purified Mannich addition products were deprotected to give the target enantiomerically pure trifluoromethylpropargylamines. A mechanistic rationale for the observed stereochemical outcome is discussed.

Merging Electrosynthesis and Bifunctional Squaramide Catalysis in the Asymmetric Detrifluoroacetylative Alkylation Reactions

An enantioselective bifunctional squaramide-catalyzed detrifluoroacetylative alkylation reaction has been developed under electrochemical conditions. The unified strategy based on this key tandem methodology has been divergently explored for the asymmetric synthesis of fluorine-containing target molecules with good stereocontrol (up to 95 % ee). Furthermore, this asymmetric catalytic reaction combines the benefits of electrosynthesis and organocatalysis for the preparation of biologically relevant products containing C-F tertiary stereogenic centers.

Detrifluoroacetylative in Situ Generated Cyclic Fluorinated Enolates for the Preparation of Compounds Featuring a C-F Stereogenic Center

Practical methods for the preparation of selectively fluorinated compounds are in extremely high demand in nearly every sector of the pharmaceutical and agrochemical industries. Here we provided an account of the recent methodological breakthrough dealing with detrifluoroacetylative in situ generation of cyclic fluoro-enolates and their application for the preparation of various polyfunctional compounds featuring quaternary C-F stereogenic carbon. The reactions include aldol, Mannich, Michael addition reactions, S_N2/S_N2' alkylations, and the additions to azo compounds. The detrifluoroacetylative protocol for in situ generation of cyclic fluoro-enolates is operationally simple and scalable and proceeds at ambient temperature. Generally, the stereochemical outcome, controlled by the stoichiometric chiral auxiliary of the chiral catalyst, is synthetically useful, allowing preparation of enantiomerically pure compounds of high pharmaceutical potential.

Catalytic Asymmetric Mannich Reaction of α-Fluoronitriles with Ketimines: Enantioselective and Diastereodivergent Construction of Vicinal Tetrasubstituted Stereocenters

Diastereodivergent and enantioselective conversion of isatin ketimines to α-fluoro-β-aminonitriles with vicinal tetrasubstituted stereocenters is achieved by a chiral copper complex/guanidine base catalyzed Mannich reaction with proper choice of the bisphosphine ligand. The reaction is broad in scope, scalable, and provides efficient access to a series of 3-aminoindolinones exhibiting a quaternary carbon-fluorine stereocenter with high yields and stereoselectivities. Selective transformations of the Mannich reaction products into multifunctional 3-aminooxindoles without erosion of enantiomeric and diastereomeric purity highlight the synthetic utility.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

This review article provides a summary of the detrifluoroacetylativein situgeneration of fluorine-containing enolates and their related reactions.

Palladium-Catalyzed Asymmetric Allylic Alkylations of Colby Pro-Enolates with MBH Carbonates: Enantioselective Access to Quaternary C-F Oxindoles

Owing to the innovative applications of fluorinated compounds in many areas of technology and medicine, methods for the preparation of C-F quaternary fluorine containing compounds are in extremely high demand. Here, we report the discovery of a general procedure for an S_N 2 reaction catalyzed by Pd/Ding-SKP-type ligands, and that occurs between Colby pro-enolates with MBH carbonates to afford the corresponding products featuring two consecutive stereogenic carbons, including a C-F quaternary stereogenic center. The reactions readily occur at ambient temperatures with high chemical yields and in excellent chemo-, diastereo- and enantioselective manners. This practically attractive stereochemical outcome, coupled with the operational simplicity and structural generality, bodes well for the synthetic application of this process in the preparation of a novel class of biologically relevant fluorine-containing compounds.

Modern Approaches for Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers: Synthetic Challenges and Pharmaceutical Needs

New methods for preparation of tailor-made fluorine-containing compounds are in extremely high demand in nearly every sector of chemical industry. The asymmetric construction of quaternary C-F stereogenic centers is the most synthetically challenging and, consequently, the least developed area of research. As a reflection of this apparent methodological deficit, pharmaceutical drugs featuring C-F stereogenic centers constitute less than 1% of all fluorine-containing medicines currently on the market or in clinical development. Here we provide a comprehensive review of current research activity in this area, including such general directions as asymmetric electrophilic fluorination via organocatalytic and transition-metal catalyzed reactions, asymmetric elaboration of fluorine-containing substrates via alkylations, Mannich, Michael, and aldol additions, cross-coupling reactions, and biocatalytic approaches.

Catalytic asymmetric aldol addition reactions of 3-fluoro-indolinone derived enolates

Reported herein is a Cu(i)/bisoxazoline ligand-catalyzed aldol reaction of unprotected tertiary enolates generated in situ from 3-(1,1-dihydroxy-2,2,2-trifluoroethyl)-substituted derivatives of 3-fluoro-2-oxindoles. A range of α-fluoro-β-aryl/hetaryl/alkyl-β-hydroxy-indolin-2-ones containing C-F quaternary stereogenic centers of high pharmaceutical importance were furnished in good yields and satisfactory diastereo- and enantioselectivities. The reactions were conducted under operationally convenient conditions and displayed wide substrate/functional group generality including unprotected N-H on the tertiary enolates, and aromatic, hetero-aromatic and aliphatic aldehydes.

Organocatalytic Asymmetric Synthesis of α-Oxetanyl and α-Azetidinyl Tertiary Alkyl Fluorides and Chlorides

Asymmetric thiourea and squaramide catalysis provides access to synthetically versatile α-oxetanyl and α-azetidinyl alkyl halides exhibiting a tetrasubstituted chiral carbon center with high yields and enantioselectivities. The products are readily transformed with negligible erosion of enantiopurity and excellent diastereoselectivity to a diverse group of multifunctional compounds including fluorooxindoles with two contiguous chirality centers, fluorinated heterocyclic spiranes, and polyspiro compounds.

Organocatalytic Stereoselective Synthesis of Fluorinated 3,3'-Linked Bisoxindoles

A highly diastereoselective organocatalytic method that produces 3-fluoro-3'-hydroxy-3,3'-bisoxindoles and the corresponding 3-fluoro-3'-amino derivatives having two adjacent chirality centers from fluorooxindoles and isatins in high yields is described. The reaction occurs in protic solvents at room temperature, it can be upscaled without compromising yield and stereoselectivity, and chromatographic product purification is not required.

Catalytic cascade aldol-cyclization of tertiary ketone enolates for enantioselective synthesis of keto-esters with a C-F quaternary stereogenic center

The first asymmetric catalytic aldol-cyclization reaction of detrifluoroacetylatively in situ generated enolates with methyl 2-formylbenzoate is reported. This reaction tolerates a wide range of substrates, affording fluorinated quaternary stereogenic α,α-dialkyl/cyclo-alkyl-β-ketoesters with good yields, high diastereo- (94% de) and enantioselectivity (96% ee) at room temperature.

Stereoselective Synthesis of 3,3'-Bisindolines by Organocatalytic Michael Additions of Fluorooxindole Enolates to Isatylidene Malononitriles in Aqueous Solution

A highly diastereoselective organocatalytic reaction for the synthesis of fluorinated 3,3'-bisindolines exhibiting adjacent tetrasubstituted carbon stereocenters is described. A broad variety of heterochiral bisindolines was prepared in 91-99% yield using 3-fluorooxindoles and isatylidene malononitriles in the presence of catalytic amounts of triethylamine in water or aqueous solution. The reaction can be upscaled without compromising yield and diastereoselectivity and the general usefulness of this method was demonstrated with various Michael acceptors and extended to aldol and Mannich reactions.

Catalytic Enantioselective Michael Addition Reactions of Tertiary Enolates Generated by Detrifluoroacetylation

This work describes, for the first time, Michael addition reactions of tertiary fluoro-enolates in situ generated by detrifluoroacetylation with 1-(1-(phenylsulfonyl) vinylsulfonyl)benzene. Excellent enantioselectivity and chemical yields were achieved with application of catalysts (10 mol %) derived from Cu(OTf)₂ and (1S,2S)-1,2-diphenylethane-1,2-diamine. These reactions show a considerable degree of structural generality and allow the preparation of new types of biologically relevant molecules that contain quaternary C-F stereogenic carbon atoms and feature five-, six-, or seven-membered rings as well as heterocyclic 3-fluoro-2,3-dihydrochromen-4-one moieties.

Stereoselective Coupling of N-tert-Butanesulfinyl Aldimines and β-Keto Acids: Access to β-Amino Ketones

The reaction of chiral N-tert-butanesulfinyl aldimines with β-keto acids under basic conditions at room temperature proceeds with high levels of diastereocontrol, leading to β-amino ketones in high yields. Based on DFT calculations, an eight-membered cyclic transition state involving coordination of the lithium atom to the oxygens of carboxylate and sulfinyl units was proposed, being in agreement with the observed experimental diastereomeric ratios. The synthesis of the piperidine alkaloid (-)-pelletierine was successfully undertaken in order to demonstrate the utility of this methodology.

Asymmetric synthesis of C–F quaternary α-fluoro-β-amino-indolin-2-ones via Mannich addition reactions; facets of reactivity, structural generality and stereochemical outcome

An asymmetric detrifluoroacetylative Mannich reaction between in situ generated tertiary enolates and sulfinyl-imines has been explored. The reaction provides a new access to α-fluoro-β-amino-indolin-2-ones with tetrasubstituted fluorinated stereogenic center.

Highly efficient synthesis of chiral quaternary 3-aminooxindoles promoted by zinc(ii) chloride via Et2Zn-catalysed addition of Grignard reagents to isaltin-derived N-tert-butanesulfinyl ketimines

An approach to chiral quaternary 3-aminooxindoles via Et₂Zn catalyzed diastereoselective addition of various Grignard reagents to broad isaltin-derived N-tert-butanesulfinyl ketimines promoted by zinc(ii) chloride.

Metal-free nitroxyl radical-mediated β-C(sp3)–H amination of saturated ketones with heteroaryl halides: multiple roles of TEMPO

The first metal-free nitroxyl-radical-mediated β-amination of saturated ketones by using heteroaryl halides as amide precursors has been developed.

Catalytic Enantioselective and Diastereoselective Allylic Alkylation with Fluoroenolates: Efficient Access to C3-Fluorinated and All-Carbon Quaternary Oxindoles

Synthetically versatile 3,3-disubstituted fluorooxindoles exhibiting vicinal chirality centers were obtained in high yields and with excellent enantio-, diastereo-, and regioselectivity through catalytic asymmetric fluoroenolate alkylation with allylic acetates. The reaction proceeds under mild conditions and can be scaled up without compromising the asymmetric induction. The unique synthetic usefulness of the products is highlighted by the incorporation of additional functionalities and the formation of 3-fluorinated oxindoles exhibiting an array of four adjacent centers of chirality. A new C-F bond functionalization path that provides unprecedented possibilities for the stereoselective generation of a chiral quaternary carbon center in the alkaloid scaffold is introduced.

Detrifluoroacetylative Generation of Halogenated Enolates: Practical Access to Perhalogenated Ketones and Alkenes

Sequential chlorination/fluorination of aromatic trifluoroacetylated ketones gives 1-aryl 2-chloro-2,4,4,4-tetrafluoro-butan-1,3-dione hydrates that are used for the synthesis of ketones and alkenes exhibiting a terminal bromochlorofluoromethyl group. The hydrates undergo detrifluoroacetylative cleavage and subsequent bromination in the presence of a copper(II)bisoxazoline catalyst, K2CO3 and NBS at room temperature. The corresponding bromochlorofluoromethyl ketones can be applied in Wittig and Horner-Wadsworth-Emmons reactions and dibromoalkenylations.

Detrifluoroacetylative in Situ Generation of Free 3-Fluoroindolin-2-one-Derived Tertiary Enolates: Design, Synthesis, and Assessment of Reactivity toward Asymmetric Mannich Reactions

The discovery of detrifluoroacetylative in situ generation of a new type of fluorinated amide enolates derived from 3-fluoroindolin-2-one and their asymmetric Mannich additions with sulfinylaldimines bearing fluoroalkyl groups is reported, which afforded α-fluoro-β-(fluoroalkyl)-β-aminoindolin-2-ones containing C-F quaternary stereogenic centers with excellent yields and high diastereoselectivities.

Construction of Vicinal Tetrasubstituted Stereocenters with a C-F Bond through a Catalytic Enantioselective Detrifluoroacetylative Mannich Reaction

An efficient asymmetric detrifluoroacetylative Mannich reaction of 2-fluoro-1,3-diketones/hydrates with isatin-derived ketimines catalyzed by a chiral copper(II)-diamine complex has been realized. The reaction afforded a series of 3-substituted 3-amino-2-oxindoles bearing fluorine-containing vicinal tetrasubstituted stereocenters in high yields (up to 99%) with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to 94% ee).